1. Field of the Invention
This invention relates to a method of making coke in coking chambers of a coke-oven battery and is particularly concerned with the control of the combustion gas supply to the burners of the battery. The invention also provides a method of measuring the temperature of hot coke.
2. Description of the Prior Art
A coke-oven battery has a number of coking chambers. Between each pair of adjacent coking chambers, there is a combustion wall containing a plurality of combustion chambers. Combustion of gas takes place in the combustion chambers to provide the heat required for the coking process. A battery may have a great many, e.g. in the order of a thousand, combustion chambers. Below the coking chambers and the combustion chambers there are regenerators in which waste heat from the burned combustion gases is used to heat the incoming combustion air. Each regenerator is periodically switched over from heating air to being heated by hot gases.
In the preparation of coke, by a batch process, coking coal is dry-distilled in the coking chamber for a period of time called the coking time. During the coking time, the temperature of the charged load of coal, hereinafter called coke cake, rises more rapidly near the combustion walls than in the middle. The coke cake is pushed out of the coking chamber after the expiry of the coking time (this operation is called pushing) and transferred to a quenching car via a so-called coke guide. Then the hot coke is conveyed in the quenching car to a quenching installation and quenched with water.
The control of the heat supply in the coking process can be considered at three levels, going from the smaller scale to the larger;
the combustion chamber level PA1 the combustion wall level PA1 the battery level.
At the combustion chamber level what matters is that each combustion chamber should have the right temperature with respect to the other combustion chambers of the same combustion wall. This is a matter of a correct distribution of gas between the combustion chambers of a combustion wall. Correction of a combustion chamber is an incidental operation and is effected by the readjustment of louvre bricks and cleaning or repair of the refractory structure.
At the combustion wall level what matters is that each combustion wall should have the right temperature with respect to the other combustion walls of a battery. This is a matter of a correct distribution of gas between the combustion walls of a battery. Correction of a combustion wall is effected by adjustment of the gas supply, e.g. using a diaphragm valve, cleaning of supply lines, shut-off valves etc.
At the battery level it is a matter of supplying the correct amount of heat. Correction is effected by adjustment of the total quantity of gas.
The temperature of the coke cake rises during the coking time. During the operation of the battery, a pushing sequence is used, e.g. for five chambers the order 1-3-5-2-4. The coking chambers are thus filled and pushed in a certain sequence. As a result, the state at any moment of the coking processes in the different coking chambers is very varied. Finally the temperature of parts of the coking battery structure varies due to the periodic switching over of the regenerators. In controlling the coking process, use is made of temperature measurements carried out on the coke-oven battery structure. In interpreting the results of these temperature measurements, allowance must be made for the above-mentioned temperature cycles and this makes the control of the coking process at the three levels mentioned above more difficult.
For many years temperatures in the combustion chambers have been measured for the purpose of control of the coking process, using an optical pyrometer. The difficulty with this measuring method is the low accuracy of the result. The measurement is really only useful for control at the combustion chamber level when nothing better is available.
GB-A-1,393,046 describes a method of the control of the battery temperature, in which it is sought to maintain a time-averaged constant value of the battery temperature. In this method the temperature of the regenerator checkerwork is measured and held constant by adjusting the gas supply. This control at battery level is an open regulation of the coke temperature at the end of the coking time. FR-A-2,318,918 describes a method of combustion control of the same type, in which flue temperatures are measured.
From EP-A-0025630 it is known to measure the temperature of the coke in the quenching car using an infrared sensor. During the transfer of the coke from the coking chamber to the quenching car, the coke is distributed along the length of the quenching car from the coke side towards the machine side (these are the two sides of the battery). The coke cake collapses vertically, so that the temperature differences in the vertical and width direction of the coke cake are evened out. In the method disclosed in EP-A-25630 the measurement of coke temperature in the quenching car is used for the location and adjustment of combustion walls with a deviant mean temperature (control at the combustion wall level) and for location and adjustment of combustion chambers with a deviant temperature (control at the combustion chamber level). The infrared sensor measures the surface temperature of the coke in the quenching car. Its aperture angle and height above the quenching car are such that it views a substantial part of the width of the coke in the quenching car.
Expert opinion has been that it is desirable to aim to keep the temperature constant at the levels of the combustion chamber, combustion wall and battery. A difficulty in this strategy is that the temperature of the coke cakes at pushing varies considerably.